Sweat School

It’s probably wise to not sweat the small stuff, but if you want to ride well and feel great (or in some cases just finish), you need to sweat— and make sure you keep sweating. Here’s a look at what’s pouring out of your pores.

Sweat keeps you cool. Your body’s initial response to warmth is to open up the blood vessels in the skin, allowing the heat to simply radiate off you into the air— but that only works to a point. When it’s hot enough or you’re working hard enough to raise your core temperature 0.3C above normal, your body begins wetting down your skin so the moisture can evaporate to cool you off. Appalachian State University thermal physiology researcher Caroline Smith, PhD. tells us more.

Your sweat glands pull fluid from your blood plasma (the watery part of your blood). That fluid is then released through an intricate biological sprinkler system comprised of approximately 2.6 million sweat glands throughout your body.

You have two types of sweat glands: eccrine and apocrine. “Sweat stimulated by an increase in body temperature is produced by eccrine sweat glands,” says Smith, while sweat caused by tense meetings with your boss, first dates, and other psychological stress is produced by apocrine sweat glands. Ecrine glands are all over your body, while apocrine glands are mainly located on the soles, palms, and armpits.

By nature, nervous sweat stinks more than exercise sweat because it’s excreted with fats and proteins, which the bacteria on your skin will metabolize, giving off the unpleasant odor we recognize as B.O.

But, because everyone has different kinds and amounts of bacteria on their skin, some people will smell more strongly than others. You also might smell differently depending on what you’ve consumed lately (particularly garlic, onions or booze). Caffeine also revs up your apocrine glands, so those preride doppios may leave you smelling not quite like roses. Finally, you might stink more if you’re cutting carbs. Low carb diets kick your body into a state of ketosis, where it breaks down protein and fat for energy. One byproduct of this process is acetone, which smells like ammonia.

The exercise-induced sweat you’re dripping all over your top tube is mostly water, but it also includes some minerals, like sodium, potassium, and chloride. When the water in your sweat evaporates, it takes heat with it and leaves behind the salt it came out of your skin with. But some peoples’ sweat is genetically saltier than others, which is why your riding buddy might look like he lost a fight with a powdered doughnut while you’re relatively uncaked.

How much sodium you excrete also changes depending on how fit and acclimated to the heat you are, says Smith. “Endurance training and heat acclimation modify your fluid regulation,” she says. Your total blood volume increases, as do hormones that regulate fluid and sodium loss, so with proper training you’ll eventually lose less sodium as you sweat.

Regardless of where you fall on the sweat spectrum, you need to stay on top of your sodium loss. Sodium is a key electrolyte—a dissolved charged particle in your bloodstream—that helps modulate fluid, nutrient, and waste exchange between your cells and the surrounding fluids. It also aids nerve impulses that keep your muscles firing. So choose a drink with about 300 to 400 mg of sodium per 16 ounces to help replace what you lose.

That all depends on how hot it is, how hard you’re working, your body size, your fitness level, and even your gender. The average person sweats about .8 to 1.4 liters an hour, with a maximum of 3 liters an hour. Over time, even if you fall on the on the low end of the sweat spectrum, those losses can really add up. In one study of more than two dozen cyclists competing in a 164K (102 mile) road race, sweat losses ranged from 4.9 to 12.7 liters over the course of the event.

Dina Griffin, RD, CSSD, CISSN, at eNRG Performance based out of Littleton, Colorado, says it can be helpful to periodically perform a sweat rate test, to see where you stand.

Griffin implements a precise testing protocol with her athletes that includes recording myriad factors including power output, heart rate and humidity. But you can ballpark your sweat rate by weighing yourself before and after a ride

Eat and drink normally heading into the test. Use the bathroom before you start. Weigh yourself nude before you kit up. Then ride for an hour or two, being sure to keep track of how much fluid you consume. When you’re done, strip down, towel off and weigh yourself again. Use the following formula to calculate your sweat rate:

“I recommend doing sweat rate tests periodically since losses can change throughout the training seasons even if all other variables remain constant,” says Griffin.

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How Much Should I Replace?

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The upper limit you can absorb is about 30 to 40 ounces an hour, so don’t attempt to replace every ounce—it’s not necessary or safe. If you know your sweat rate, aim to replace about 75% of what you lose, recommends Monique Ryan, RD, author of Sports Nutrition for Endurance Athletes.

As a good ballpark, research shows that replenishing about a bottle’s worth (20 to 24 ounces) of fluid an hour does the trick. That means sipping about 5 to 6 ounces (two to three gulps) every 15 minutes or so while you’re out riding. Bigger riders may need more; smaller riders may need less, and everyone may need a bit more when the temperatures are over 75 degrees. Generally speaking your thirst is a good guide.

Any other benefits of a good sweat? Well, a good sweat opens up your pores and releases the grime that’s trapped in there, so it’s good for your skin. Just be sure to wash all that dirt off your face when you’re done.

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